1. Field of the Invention
This invention relates to wireless communication systems and to a method and system for using such a system in a Frequency Division Duplexing region.
2. Description of Related Art
A wireless communication system facilitates two-way communication between a plurality of subscriber units (fixed and portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The key objective of these wireless communication systems is to provide communication channels on demand between the plurality of consumer subscriber units and their respective base stations in order to connect the subscriber unit user with the fixed network infrastructure.
Subscriber units typically communicate through a node with the base station using a “duplexing” scheme thus allowing the exchange of information in both directions of connection. Transmissions from the base station to the nodes are commonly referred to as “downlink” transmissions. Transmissions from the nodes to the base station are commonly referred to as “uplink” transmissions. In wireless systems having multiple access schemes a time “frame” is used as the basic information transmission unit.
Depending upon the design criteria of a given system, systems have typically used either time division duplexing (TDD) or frequency division duplexing (FDD) methods to facilitate the exchange of information between the base station and the nodes. In a TDD communication system, the base station and the nodes use the same channel, however, their downlink and uplink transmissions alternate one after the other to prevent interference. In a FDD communication system, the base station and the nodes use different channels for their downlink and uplink transmissions, respectively. Thus, the concern for interference between uplink and downlink transmissions is mitigated in a FDD communication system as compared to a system using TDD. However, the increased cost and complexity in deploying a FDD communication system often outweighs this obvious advantage over a TDD communication system.
In both TDD and FDD systems, each base station and node includes a modem connected to an outdoor unit (“ODU”). The modem is configured to modulate an outgoing signal and demodulate an incoming signal. If the modem is configured to modulate and demodulate simultaneously, the modem is a “full-duplex” modem. If the modem is not configured to modulate and demodulate simultaneously, but rather switches between modulating and demodulating, the modem is a “half-duplex” modem. Similarly, the ODU can be configured as a full-duplex or half-duplex ODU. A full-duplex ODU is configured to transmit an outgoing signal and receive an incoming signal at the same time. A half-duplex ODU would alternate between transmitting and receiving.
In an exemplary FDD communication system, the modem and ODU operate simultaneously to transmit and receive information. Since this occurs simultaneously, any subcomponents that might be common to the transmit and receive signal paths through the modem and ODU are not shared. In contrast, since the modem and ODU in an exemplary TDD communication system are half-duplex, components which may be common to the transmit and receive paths can be shared. Such sharing reduces the cost of the system.
As opposed to allowing each region to select an FDD or TDD communication protocol based on such advantages and disadvantages, certain specific regions are restricted by communication regulations. These communication regulations often mandate the use of different channels, i.e. frequency bands, for uplink and downlink communications similar to an FDD communication system. For example, in Germany, a 26 GHz band is FDD oriented since the uplink channel and downlink channel are clearly defined. In a typical case, a service provider is granted 2 or 4 channel pairs (2×28 MHz each) and is required to maintain a channel separation between the uplink and downlink channels.
By requiring a service provider to use different uplink and downlink channels, there is little incentive to use half-duplex modems or ODUs. If an exemplary halfduplex modem or ODU were used, a significant loss in bandwidth would be incurred.
Consequently, there is a need for a system and method that allows the use of half-duplex modems and half-duplex ODUs in an FDD communication system. Furthermore, this system and method should simplify the re-use of available channels and limit co-channel interference between multiple base stations or multiple nodes in such a region.